1. Technical Field
Embodiments of the subject matter disclosed herein relate generally to apparatuses, methods and systems and, more particularly, to mechanisms and techniques for monitoring vessels or containers configured to hold materials having an elevated temperature.
2. Discussion of the Background
Metallic vessels or containers of various sizes and shapes designed to hold materials at elevated temperatures are widely used in many industrial applications. Example of these applications include, but are not limited to, gasification processes in chemical and power production, Electric-Arc Furnaces (EAF), Basic Oxygen Furnaces (BOF), ladles, blast furnaces, degassers, and Argon-Oxygen-Decarburization (AOD) furnaces in steel manufacturing. As known in the art, these containers are normally lined with refractory material installed, in brick form or cast in monolithic blocks in order to protect the metallic part of the vessel from the high-temperature contents placed therein; however, due to normal wear and tear of the refractory material through the combined effects of oxidation, corrosion and mechanical abrasion, some portion of the refractory surface in contact with the molten metal is lost during processing, thus requiring frequent inspection so as to assure extended use by performing early localized repair in order to avoid catastrophic failures and unnecessary or premature refurbishment of the entire vessel's refractory lining.
Before the advance of optically based inspection techniques, inspection of ceramic linings to detect unacceptable levels of lining thickness was performed visually by an experienced operator looking for dark spots in the lining indicating either high localized heat transfer rates to the refractory material and metallic shell or possible excessive wear and the need for lining repair. Such an approach introduces a combination of art and science, exposes the container operator to unnecessary industrial hazards, reduces the frequency of inspections, and lacks the desired accuracy. In addition, costs associated with the installation and repair of ceramic linings have increased significantly over the past twenty years as refractory materials have been reformulated for application-specific installations. In order to improve the efficient use of these more expensive refractory materials, several conventional techniques have been developed to minimize the above-summarized risks including those configured to measure directly the wear on the refractory material and those adapted to measure the effect of the refractory wear on the metallic vessel, such as for example, the indirect monitoring of heat transfer rates to the vessel. However, as summarized below, these conventional techniques have several limitations.
As to conventional techniques configured to measure quantitative refractory wear directly by use of a laser, for example, because the diameters of the lasers are of finite sizes (e.g., approximately 40 to 60 mm in some applications), potential refractory defects with characteristic dimensions smaller than the laser beam diameter, such as a small hole in the lining, are very difficult, if not impossible, to detect, making the localized piece of missing brick also difficult to detect. Moreover, because of the high angle of incidence between the laser beam and the ladle walls, the size of the hole, when one is detected, appears to the operator or laser scanner to be smaller than it actually is.
In addition, localized slag buildup on interior ladle surfaces may make it difficult to detect areas were lining repairs may be needed. That is, as steel is drained from the ladle, the small amount of slag carried over from converter tapping or introduced at the ladle metallurgy furnace can form a coating on the walls or bottom of the ladle. Because much of the accreted slag dissolves into the next ladle heating cycle, comparison of heat-to-heat measurements can sometimes reveal slag accumulation in a prior measurement. However, for any single heat, techniques that use lasers are not capable of resolving the difference between remaining refractory and slag build-up on the interior ladle surfaces. As such, in the presence of slag accumulation, the system will over-predict the lining thickness or under predict the amount of lost refractory—both undesirable limitations in practice.
Finally, another potential problem that may not be detected by laser-based system is the result of fining, which occurs when molten steel naturally enters small gaps (e.g., small openings with a characteristic dimension of approximately 1-5 mm) that develop between the bricks in a refractory-lined vessel. As understood by those of ordinary skill in the arts, fining has the potential to eventually form a metal bridge between the molten metal contained in the ladle and the solid metallic outer shell. Minor finning only causes localized heating of the ladle shell. However, with time, minor fining may become severe and result in melting of the ladle shell and subsequently leakage of molten steel. Thus, while conventional contouring systems are a useful tool to characterize the interior profile of the vessel, there are situations in which the apparent thickness measurement alone may not be sufficient to prevent breakouts.
Examples of conventional techniques configured to measure the qualitative effect of refractory wear on the metallic vessel are those adapted to estimate the temperature on the outside surfaces of the vessel. As the internal refractory material wears and becomes thin, the temperatures of the metal shell in the compromised areas increase due to the increased heat transfer from the molten materials to the vessel. Such measurements are typically done with the ladle hanging from a crane, shortly after the ladle leaves a slab caster, and are used primarily to determine when the container should be removed from service. This qualitative measurement gives an indication of hot spots on the ladle shell independent of the cause (i.e., impending failures due to thinning of the lining, or finning, or both) and, as such, are a direct measure of the nominal health of the “containment.” However, those of ordinary skill in the applicable arts will understand that these techniques only provide qualitative information and are not capable of providing detailed information characterizing the wear rate of the lining itself. The local thickness of the refractory lining, the possible existence of finning effects, the time that the molten metal was contained in the ladle, the temperature history of the molten material while it was in the ladle, the processing history (i.e. via ladle metallurgy furnaces) of the molten material while in the ladle, and the radiative properties of the ladles' exterior surface all contribute to the apparent temperature of the metal shell. Thus, the external temperature measurements are only useful on a relative basis, and the lack of quantitative information in the data precludes determination of wear rates and refractory optimization in the ladle.
Therefore, based at least on the above-noted challenges of conventional techniques, what is needed are devices, systems, and methods that will minimize or eliminate inconsistencies in the measured data of refractory lining and external surface temperature of metallic vessels configured to carry materials at temperatures above the melting point of the metal. This will allow the early detection and inspection for molten metal creep or small holes in the lining—all of which can contribute to lining, failure, thereby increasing operational safety while reducing operating costs associated with expensive cleanup operations and potential production down time.